Described below is a switching apparatus for alternately connecting a mobile radio module and an E-Call controller to a shared antenna. As a result, the antenna can be used by the mobile radio module and coupled to the E-Call controller if required.
An E-Call controller can be used to send an emergency call (or E-Call for short). The E-Call controller triggers this emergency call automatically if the motor vehicle is involved in an accident. The E-Call controller can be activated e.g. by a trigger signal from a crash sensor system. The emergency call can be used to transmit e.g. information about the current position of the motor vehicle to a control center. Furthermore, a telephone connection can be provided between the control center and the passenger compartment of the motor vehicle. This allows a person who is in the motor vehicle to communicate with the control center without having to operate the telephone himself.
Provision of a mobile radio connection, which is required for the emergency call, between motor vehicle and e.g. the control center requires an antenna that can be used to send the emergency call to a telephone network. Since an E-Call is a safety application, it is of interest to allow a mobile radio connection that is as robust and has as little interference as possible. A demand on the antenna is therefore that it be positioned so as to be as accident-proof as possible with the best possible performance. In this regard, there are only a few antenna positions that fulfill this as such. One possible position that ensures a good compromise solution between safety in the event of a crash and the best possible performance is the roof antenna. This is also very advantageous for use by a mobile radio module for telephone and online services, however. If this optimized position and antenna were to be used exclusively for an E-Call controller, this would inevitably mean impairment of the other services, that is to say telephone and online services, since it would be necessary to resort to other antennas for these. Interconnection by a simple coupler or switch is not readily possible at this location, since the inadequate decoupling means that there is the risk of the input stages of the two reception modules (mobile radio module and E-Call controller) damaging one another.
DE 10 2007 058 985 A1 discloses a motor vehicle in which an antenna is alternately connected by a switch to a mobile radio telephone, on the one hand, and an entry control system for keyless entry to the motor vehicle, on the other hand. If the entry control system uses the antenna, the mobile radio telephone is electrically isolated from the antenna by the switch, so that a coaxial cable that connects the mobile radio telephone and the switch ends in an open-ended line. Before the mobile radio telephone is isolated from the antenna, it is made certain that there is nobody in the motor vehicle, so that operation of the mobile radio telephone is unlikely.
The open-ended line results in the problem that, from the point of view of the mobile radio module, the connection between mobile radio module and antenna is interrupted, as may also be the case if the coaxial cable is faulty. In other words, from the point of view of the mobile radio module, decoupling of the coaxial cable from the antenna produces a connection fault.
DE 10 2010 028 871 A1 discloses an antenna device for vehicle communication. The antenna device has the E-Call unit or emergency call unit integrated in the mobile radio module, so that it is unnecessary for mobile radio module and E-Call controller to be coordinated, as a result.
DE 10 2013 215 728 A1 discloses a method for selecting a radio transmission channel in a radio system. Each radio transmission channel has a different transmission technology. Selection of the radio transmission channel optimizes the respective connection technology and/or infrastructure component in terms of the respective application and hence the quality. For an emergency call function, it is possible for a particularly high priority to be set, so that the emergency call function always provides the transmission technology having the highest quality.
US 2005/0231439 A1 describes an antenna switching device that can be used to route radio-frequency signals via a respective signal input to an antenna alternately. The other signal, which is not routed to the antenna, in each case is channeled off to a ground potential via a resonant circuit. This prevents this blocked signal, which is not forwarded to the antenna, from interfering with the other signal.